Loosen slightly the two rear spindle nuts and the brake' anchor pin S36-23AC. Now turn the adjusting screws so that each side is moved an equal distance. Tighten up the spindle nut, then the wheel should be central between the stays. The chain should have about 1/2" up and down play midway between the sprockets.
To test the alignment of the back wheel, stretch a string tightly alongside the front wheel. Turn the front wheel till the string touches both edges and adjust the back wheel with the adjusting screws until it touches the string also on both edges.